The present invention relates to a permanent-magnet excommutator motor which has a ferromagnetic auxiliary pole with a high permeability formed as a U-shaped bracket and arranged on a stator yoke in a gap between two permanent magnet poles of a low permeability.
Motors of the aforementioned general type are known in the art. One of such motors is disclosed, for example, in the U.S. Pat. No. 3,083,310. In the embodiment described in this patent the permanent magnets are secured by a U-shaped bracket of steel which is welded on a tubular stator yoke. The DE-OS No. 2,512,273 discloses a permanent-magnet excited commutator machine which has permanent magnet poles of a low permeability and U-shaped auxiliary poles of ferromagnetic materials with a high permeability. The auxiliary poles are located in the interpolar gaps and form stray webs for the armature transverse field. Thereby the machine obtains series connection behavior, since with increasing armature current, an increasing armature transverse field is obtained which during operation of the motor produces an additional flux through the stray pole. Thus an excitement field dependent on a current is produced, which is required for the series connection behavior.
The EP-A1 No. 48,966 discloses a motor in which, for obtaining a series connection behavior with permanent-magnet excited motors, a ferromagnetic auxiliary pole is arranged at the side of a permanent magnetic segment. It is mounted by gluing at that end of the permanent magnet segment which lies at the leading tip of the armature. The dimension of the auxiliary pole must be such that it occupies approximately 20 percent of the pole pitch. Iron is preferrably used as a ferromagnetic material for the auxiliary pole; it has a high permeability, so that with increasing armature current it takes charge of the stray flux through the armature transverse field. Thus the motor torque increases with high load, but particularly during starting of the motor.
Motors are also disclosed in U.S. applications Ser. Nos. 085,513; 166,251; 179,280; 815,073; 825,002; 884,637; 934,546 and U.S. Pat. No. 4,155,021 of the same inventor.